Hot bearing indication apparatus



Feb. 10, 1953 P. s. JOHNSON ET AL 2,623,344

HOT BEARING INDICATION APPARATUS Filed July 15, 1948 5 Sheets-Sheet 1 INVENTORS Paul .5. Johnson cmd L HY fiM SW9 THEIR A TTOIZZVEY' Feb. 10, 1953 P. s. JOHNSON ET AL ,3

HOT BEARING INDICATION APPARATUS Filed July 15, 1948 3 Sheets-Sheet 2 Ip Zn 412 5); 6n -2 5 A Iago Z012 4602 250 -6m INVENTORS Paul 5. Ila/2125012 and THEIR ATTORNEY Patented Feb. 10, 1953 HOT BEARING INDICATION APPARATUS Paul S. Johnson, Washington, D. 0., and Lester E. Spray, Wilkinsburg, Pa., assignors to Westinghouse Air Brake Company, a corporation of Pennsylvania Application July 15, 1948, Serial No. 38,796

8 Claims.

Our invention relates to hot bearing indication apparatus, and particularly to apparatus for indicating to railway enginemen and trainmen when an axle bearing of a railway car or locomotive is being overheated.

If an axle bearing which is being overheated is not discovered and appropriate remedial action taken promptly, the overheating may not only result in damage to the journal and its housing, but may also result in a broken axle, which might cause derailment of its car, ossibly followed by wrecking of its train.

One feature of our invention is the provision of apparatus embodying heat responsive means comprising resistors having a high positive temperature coeflicient of resistance, and also comprising resistors having a high negative temperature coefficient of resistance, for controlling hot bearing indication devices.

Another feature of our invention is the provision of apparatus embodying thermoelectric means, such for example as thermocouples, for controlling hot bearing indication devices.

Still another feature of our invention is the provision of apparatus embodying devices, which at atmospheric temperatures, are non-conductors or have high resistance to the passage of electric current of at least one polarity, but which, upon being heated a given amount above the atmospheric temperature range, become conductors of electric current.

We shall describe a few forms of apparatus embodying our invention, and shall then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing resistors having a high positive temperature ooeflicient of resistance, and other resistors having a high negative tempera ture coeificient of resistance, arranged in the journal housings of a railway car or locomotive; Fig. 2 is a diagrammatic view showing one form of apparatus embodying our invention, in which the resistors shown in Fig. 1 are used; Fig. 4 is a diagrammatic view showing a modification of the apparatus shown in Fig. 2, in which the resistors are arranged in the journal housings of a railway car or locomotive as shown in Fig. 3; Fig. 6 is a diagrammatic view showing another modification of the apparatus of Fig. 2, in which thermocouples are arranged in the journal housings s shown in Fig. 5; Fig. 7 shows a modification of the apparatus shown in Fig. 6; Fig. 8 shows another modification of the apparatus shown in Fig. 6; Fig. 9 is a diagrammatic view showing a modified form of apparatus embodying our invention, in which devices are used having high resistance to passage of current of a given polarity at atmospheric temperatures but becoming conductive at higher temperatures and are arranged as shown in Fig. 5; and Figs. 10, 11, and 12 show modifications of the form of apparatus shown in Fig. 9.

Similar reference characters refer to similar parts in each of the views.

Referring first to Fig. 1. the reference character A designates a railway vehicle of any suitable type which, a here shown, is provided with two trucks, each of which has three axles. The axles of vehicle A are designated by the reference characters I to 6, inclusive, and are provided, at their ends, with any suitable type of journal boxes 1.

Resistors each having a high positive temperature coefiicient of resistance are provided, one for each of the axles l to 6, inclusive, and are designated by the reference characters in to 6p, respectively. Other resistors having a high negative temperature coeificient of resistance are also provided, one for each of the axles l to 6, inclusive, and are designated by the reference charactor in to En, respectively. Resistors lp to 6p, inclusive, are placed to be subjected to the temperature of the hearings in boxes 7 at the ends of the axles which are adjacent a given side 8 of vehicle A, and resistors in to 6n, inclusive, are placed to be subjected to the temperature of the hearings in boxes 1 at the opposite ends of the axles adjacent the opposite side 8a of vehicle A.

In Fig. 2, the resistors for axles l to 4, inclusive, shown in Fig. l, are included in 9, Wheatstone bridge designated by the reference character IW, and the resistors for axles 5 and 6 are included in a second Wheatstone bridge designated by the reference character 2W. It will be noted that each of the resistors lp to 6p, inclusive, which has a positive temperature coefficient of resistance, is connected in a bridge arm in series with one of the resistors in to in, inclusive, which has a negative temperature coeflicient of resistance. This arrangement compensates for changes in ambient temperature. If the ambient temperature should rise, the resistance or resistor I p, for example, would increase, whereas the resistance of resistor 211 would decrease, so that the total resistance of the arm of bridge 1W which includes these two resistors would remain substantially the same. If, on the ot or hand, all the resistors had a positive temperature coefficient of resistance, or if all the resistors a negative temperature coefiicient of resistance, the total resistance of each bridge arm would vary upon variations in ambient temperature.

A coding device, designated by the reference character D, is constantly connected across a suitable source of current having terminals 3 and N. Device D therefore repeatedly opens and closes its contacts 9 and i3, so that bridge .!W is periodically unbalanced by a. shunt path in-- cluding contact 9 of coding device D across its arm which includes resistors 31; and 4p. As long as there is no abnormal heating of any of the bearings, bridge IW will be balanced during the periods when contact 9 of coder D is open.-

Pulses of current are therefore normally supplied to a rectifier iE for periodically energizing a code following relay IR during the closed periods of contact 9 of coder D. Rectifier 1E may be of any suitable design'such, for example, as the well-known copper oxide rectifier bridge type comprising half-Wave units ii, 22', 32, and ii.

Relay IR will therefore normally repeatedly close its contacts iii-- and H at their front and back points alternately for effecting ene'rgization of a decoding relay, designated by the reference character AiR; through a decoding transformer IF which has primary and secondary windings m and y, respectively. Relay AIR on account of being slow releasing, maintains its contact [2 in the open position in response to such control by relay ER, so that the indication device, shown as a bell K, remains deenergized, and therefore inactive.

We shall assume that thetemper'ature or the bearing for'axle' l, where resistor !p is located, begins to rise; The" resistance or resistor lp will therefore increase, thereby unbalancing bridge IW during the open as well as the closed periods of contact Sl'of coder D. As the overheating atresistor lp increases further, bridge IW will become unbalanced to such an extent that relay lRwilI retain its contacts it and H constantly'clo'sed at their front points;

Relay AIR is thereby deenergized, so that indication device K becomes energized by a circuit passing from terminal B, through contact i2 of relay AIR, and indication device K to terminal N. The enginemen and trainmen, in response to the indication thus given by device K, will then proceed to take appropriate action to avoid further overheating of axle with probable damage.

Resistors 1', shown in two of the arms of bridge 2W, may be placed in any suitable location on vehicle A, and each should include two portions, one of which has a positive temperature coefficient of resistance, and the other of which has a negative temperature coefficient of resistafice in order to compensate for variations in the ambient temperature".

In the arrangement. shown in Fig. 2, the resist'ors for the two ends of each axle are placed in adjacentibridgeiarms, so that ii the bearings at the same time, as sometimes happens when an axle becomes bent}. the unbalancing efiect of the resistors for the two" ends of the axle will be additive.

Referring next to Fig. 3, each alternate axle here provided with resistors each of which has a positive temperature coefficient of resistance, whereas each of the intervening axles is provided with resistors each of which has a negative temperature coeflicient of resistance. Accordingly, resistors ip and lap of axle l, resistors 3p and tap of axle 3, and resistors 5p and 50p of axle 5 have a positive temperature coehicient of resistance, whereas resistors 2n and 2am of axle 2, resistors 4n and 4cm or axle d, and resistors En and Eon of axle 5 have a negative temperature coefficient or resistance. This arrangement of the resistors compensates for any difierence in ambient temperature between the ends of the axles which are, adjacent side 8 of vehicle A and the opposite ends of the axles which are adjacent the opposite side 8a or vehicle A. If vehicle A were being moved a considerable distance over a straight stretch of track, such as on plains or desert territory, with the axle housings adjacent one side of vehicle A in the shade while those on the opposite side were in the direct sunlight, there might be a considerable diiierence in the ambient temperature between the ends of the axles adjacent the two sides of vehicle A.

The resistors located as shown in Fig. 3 are arranged in series with each other in a circuit; shown in Fig. 4, passing from the positive terminal of a suitable source of current, such as a battery lQ, through res'istors" ip to can, inclusive, and a control resistor back to battery iQ. With both the resistorsoi each axle having a positive temperature coefficient of resistance, or with both the resistors of each axle having a n gative temperature coefficient of resistance, if an axle, such, for example, as axle I should become bent, causing the temperature of both of its ends to rise, the eiiect produced by resistors lp and lap would be'additive. V V 7 With half of the total number of resistors on each side of a vehicle-having a positive'temperature coefficient of resistance; and with the other half of the resistors on each side of the vehicle having a negative temperature coefficient of resistance, compensation is provided for changes in ambient temperature, so that with no ab normal heating at either end of any axle, the voltage across resistor a1 willbe constant.

Two gas tubes, designated by the reference characters IU and 2U, such, for example, asthe well-known thyratron type, are controlled by changes in voltage produced across resistor or by changes in resistance of any of the axle resistors due to abnormal heating in the' some spending axle housing;- Usual protective resistors, designated by the reference character 4'1, are provided for the grids for these: tubes;

A negative potentiai, su'fiicie'nt to prevent plate current from flowing, is maintainedon the grid of tube ill by the normal potential drop across resistor or. A- negative' potential,- sufficient to prevent plate current how, is maintained-onthe grid of tube ill by a suitable source of current,

'such as a battery 2Q; connected in opposition to the potential drop across resistor a1; Indication relays 3R and GR are controlled by the plate circuits of tubes, EU and 2U which are supplied with current from suitable sources such as batteries 3Q and 6Q, respectively. Theplate' circuits for tubes Ill and 2U areprovided with resetting devices, here shown as push button circuit controllers iP and 2?, respectively. I

We shall assume that the resistance of resistor lp increases, due to abnormal heating in the corresponding axle housing of axle I. The drop across resistor or is thereby reduced. When this drop is sufficiently reduced, the grid of tube IU will become enough less negative to permit plate current to flow in the plate circuit for tube IU for energizing relay 3R, this circuit passing from battery 3Q through the winding of relay 3R, resetting device 5P, and tube IU, back to battery 3Q.

Relay 33, upon becoming energized, completes a circuit for energizing indication device K, this circuit passing from terminal B, through contact of relay 3R, and indication device K to terminal N. Upon taking appropriate action because of the overheating of axle l, a trainman will depress push button IP for restoring the plate circuit for tube iU to its normal condition. Relay 3R will thereupon become deenergized, causin indication device K to also become deenergized.

We shall now assume that the resistance of resistor 2n decreases due to abnormal heating in the corresponding axle housing of axle 2. The potential drop across resistor or will thereby be increased. The grid of tube IU will therefore be more negative, so that it Will remain inactive, but the grid of tube 2U will be less negative. When the resistance of resistor 2n becomes sufficiently reduced, the grid of tube 2U will become enough less negative to permit plate current to how for energizing relay 4R in the plate circuit passing from battery 4Q, through the winding of relay 4R, push button 21?, and tube 2U, back to battery 39,.

Indication device K will therefore become energized by a circuit including contact 16 of relay HR. Upon taking appropriate action in response to the indication given by device K, a trainman will depress push button 2P for resetting the plate circuit for tube 2U. Relay 4R will therefore become deenergized, causing indication device K to in turn also become deenergized.

Instead of having resistors with a high positive temperature ooefiicient of resistance for some of the bearings, and resistors with a high negative temperature coefficient of resistance for the other bearings, all these resistors could have a high positive temperature coefiicient of resistance, and resistor or could also have a high positive temperature coefficient of resistance to compensate for ambient temperature changes, or all the bearing resistors could have a high negative temperature coefiicient of resistance and resistor car could then also have a high negative temperature coefficient of resistance to compensate for ambient temperature changes.

Referring now to Fig. 5, the heat responsive devices here shown at each end of each axle are all alike.

In the modified form of apparatus shown in Fig. 6, heat responsive devices It, lat, 2t, Zat, etc., as shown in Fig. 5, are employed, which are of the thermoelectric type, such for example as thermocouples. The thermocouples for axles I to 4, inclusive, are arranged two in each arm of a Wheatstone bridge 3W. The two thermocouples which are included in each arm of bridge 3W are oppositely poled in order to compensate for any effect which might be produced on them I by ambient temperature conditions.

A coding device D is constantly energized from terminals B and N. Contact I! of device D is therefore repeatedly closed at its front and back points alternately. During the periods while the.

back point of contact I! is closed, bridge 3W is balanced, so that no voltage will be impressed across any of its arms if there i no abnormal heating of any axle housing. During the periods when the front point of contact I! of coding .device D is closed, a potential is supplied to bridge 3W from a suitable source of current, such as a battery 5Q, through the portion hr of a variable resistor.

This produces a potential drop across points Id and 2d of bridge 3W for energizing winding aw of an indication relay 5R through a transformer 3F, an amplifier IM, and a rectifier 3E. At the same time, there is a potential drop across points 3d and 4d of bridge SW for energizing winding Inc of indication relay 5R through a transformer 4F, an amplifier 2M, and a rectifier- 4E. Windings aw and bw are so connected that they work together to operate the contacts I 8 and 19 of relay 5R.

Relay SR is thus periodically energized in step with contact I! of coder D, so that contacts 13 and i9 oi relay 5R are repeatedly closed alternately at their front and back points. With the contacts of relay 5R thus operated, a decoding indication relay 6R will be energized through transformer 5F, so that its contact 20 will remain open, causing indication device K to remain deenergized.

We shall assume that any one of the axle housings starts to heat, so that the corresponding thermocouple produces an electric potential in bridge 3W. When this potential becomes sumciently high, relay 5R will be energized while contact I! of coding device D is closed at its back point as well as when it is closed at its front point, so that relay 5R. will retain its contacts 18 and l 9 closed at their front points, causing relay 6R to be deenergized, and indication device K to be operated by its circuit which includes contact 26 of relay 6R.

In the modified form of apparatus shown in Fig. 7, equal numbers of the thermocouples are oppositely poled in series with each other. The thermocouples for the two ends of each axle are poled in the same direction so that they will produce potential of the same polarity if both ends of the associated axle should become heated because of the axle becoming bent.

With this arrangement, if any one of the therlllOCOllplES'WhiCh is poled in the same direction as thermocouple It produces a potential because of heating of the associated axle housing, an indication relay 1R will become energized through a suitable amplifier 3M, which is arranged to be efiective for this purpose in response to potentials of only the polarity indicated on the drawing adjacent the symbol for amplifier 3M. With relay 1R energized, indication device K will be energized by a circuit including contact 2! of relay 7R.

If, on the other hand, any one of the thermocouples which is poled in the opposite direction, the same as thermocouple 2t, produces a poten tial due to its associated axle housing becoming heated, a second indication relay 8R will become energized through a suitable amplifier 4M. Indication device K will then become operated by a circuit which includes contact 22 of relay 8B.

In the apparatus shown in Fig. 8, which is a modified form of the apparatus shown in Fig. '7, gas tubes 3U and 4U, such as the well-known thyratron type, are controlled by the thermocouples. Primary winding lm of a transformer 6F isenergized from a suitable source of alternating current having. terminalsiBX and NX. The

plate circuit for tube 3U is energized from secondary winding i'y oi transformer BF, through the portion 2r of a variable resistor, and abias voltage. is supplied to the grid of tube 4U by the other portion of the same resistor. Tube ill is. similarly energized from secondary winding 2g of transformer 8F through a second variable resister which has a portion 31".

If a thermocouple which is poled in the same direction as thermocouple It produces a voltage because. the corresponding axle housing becomes abnormally heated, it will. make the. grid of tube 3U less". negative. so that. alslow release neutral. indication. relay ER. will become energized. by the plate circuit of' tube 3U. Indication device K. will, then become. energized by a-v circuit including contact- 23. of relay ER.

If; a, thermocouple. which is poled in the same direction as thermocouple l'at; produces a. poten tial due to abnormal heating of the associated.

axle housing, it'will make. the grid ofitube :lU less negative, so that a second. slow release relay 8R will become energized by the plate circuit of tube iU, With relay 8R energized, indication device 2: will then be energized by a. second circuit including contact 2 5 of relay 8R. Resetting devices shown as push buttons SP and 4P are provided for tubes SU and 4U, respectively.

In the form of apparatus embodying our. in-

vention as shown in Fig. 9, heat responsive devices, located as shown in Fig. 5, are employed of a type such as the well-known copper oxide half-wave rectifier units, which at normal-term peratureshave high resistance to. passage of current of a given polarity-but. which, upon becoming heated, become conductors for such current. Although we have shown the unitsfor only axles i, 2, and 3 connected across; the circuit. for an indication relay 9R, the'units' for axles4, 5,. and 6 may be similarly connected across the circuit for relay 9R.

,elay an is normally energized by a. circuit passing from terminal B, through a resistor h, and the winding of relay 9R, toterminal- N. With relay 9R energized, indication deviceK isdeenergized, because its circuit is openxa't' contact 25 of relay QR.

If any one of the half-wave rectifier units, such for example, as unit it, becomes conducting due to overheating or" the correspondingaxlehousing,

the winding relay 9R will be shuntedby'such unit, causing relay 91% to be deenergizedl With relay QR deenergized, indication. device?! will becperated by its circuit including. contact 25 of relay 9R.

the modified form of apparatusshown in. Fig. 1%), the heat responsive devices are of a suit.- able gas tube type which prevent the iiow of electric current at normal atmospheric temperatures, but whiclrupon becoming heated; become conducting. Relay HR is normally energized by a circuit which is similar to the circuit previously traced for relay 9R, so that" indication device K is normally deenergized. If any one of the gas tubes becomes conducting dueto: ab-

normal heating of the associated axle housing, relay 52R will become shunted by such gas, tube, causing its contact 25 to close, and to. thereby complete the circuit for operating indication device K.

In the form of apparatus shown in Fig. 11, heat responsive devices arranged as shown in Fig. 5 are employed which are of the asymmetric unit type, such as the copper oxidehalf-waverectifier.

An: indication relay is here; providedfor each.

0 asymmetric unit. We have shown only the circuits for units It and hit, for example, for controlling the corresponding relays HR and 12B. These relays are of the direct current type, which will retain their back contacts open if they are energized by direct current, but willpermit these contacts to close if alternating current is supplied to their windings.

The control circuit for each of these relays is connected across terminals BX and NX of a suitable source of alternating current. The current from one half ofthe alternating current wave is: normally shunted through the asymmetric units, whereas the relays are energized by pulsating direct current from the other half of the alternating current wave.

Relay HR, for example, is normally energized by pulsating current passing from terminal BX, through a resistor l2, and winding of relay HR to terminal NX. Pulsating current from the other half wave of alternating current passes from terminal NX, through unit It, and resistor ii to terminal BX.

If unit It should become conducting because of? abnormal heating. of the corresponding axle housing, thewinding of relay l IR will be shunted by unit it, causing relay HR to become deenergized'. and thereby complete a circuit through its contact 26 for energizing, indication device K.

In the modified form of apparatus which is shown in Fig.- 12, each asymmetric unit is connected in series with the associated indication relay, instead of in multiple as is shown in Fig. 11. Relay HR is therefore normally energized by pulsating current passing from terminal BX, through unit it, and the winding of relay HR to terminal NX. Contact 23 of relay I IR is therefore open, so that indication device l deenergized.

If unit It should become conducting in the high resistance direction because of abnormal heatingof the associated axle housing, or if it should become short-circuited, alternating current would be supplied to the winding of relay i m, from terminals X and NX, and then relay IIR- would release its contact 2%, causing indication device K to be operated. It follows that, with the form of apparatus shown in Fig. 12, any failure, as well as overheating, of an asymmetric unit, such as a short circuit, or an open circuit, will cause the hot bearing indication device K to be operated.

Although we have herein shown and described only a few forms of apparatus embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. Heat indication apparatus for two appliances comprising, in combination, a thermoelectric device ior each of said appliances each placed tobe affected by the temperature of the associated appliance, a Wheatstone bridge in one arm of which said thennoelectric devices are connected in opposition so that electric potentials generated by said thermoelectric devices oppose each other, indication means, and means controlled by the potential drop across opposite points of said bridge. for. operating said indication means in response to electric potential produced: by either of said thermoelectric devices because? of abnormal heating ofthe associated appliance;

2. Heat indication apparatus for-an appliance comprising, in 'combinatioma thermoelectric device placed to be afiected by the temperature in said appliance, a Wheatstone bridge in one arm of which said thermoelectric device is connected, means for periodically inserting an electric potential in one arm of said bridge, code following means, means controlled by the voltage drop produced periodically across opposite points of said bridge by said electric potential for odically operating said code following means, means controlled by voltage drop produced across opposite points of said bridge by said tbermoelectric device in response to abnormal heating of said appliance for constantly operating said code following means during the oif periods of said electric potential, and indication means controlled by said code following means.

3. Hot bearing indication apparatus for a plu rality oi axle bearings comprising, in combination, a thermoelectric device for each or said axle bearings each placed to be affected by the temperature of the associated axle bearing, electric circuit means including an even number of said thermoelectric devices connected in series with each other so that electric potential produced by any one of a given half of said even number of thermoelectric devices is in a given direction in said circuit means and electric potential produced by any one of the other half of said even number of thermoelectric devices is in the opposite direction, indication means, and means controlled by any one of said thermoelectric devices for effecting operation of said indication means if the corresponding axle bearing becomes abnormally heated.

4. Heat indication apparatus for a plurality of elements comprising, in combination, a plurality of thermo-electric devices one for each of said erielements, each of said thermo-electric devices w placed to be controlled to generate an electric potential in response to abnormal heating of the corresponding one of said elements, a control circuit arrangement in which a given number of said thermo-eleotric devices are connected in series to supply an electric potential in a given direction and an equal number of said thermoelectric devices are connected in series with each other and with said given number of said thermoelectric devices to supply an electric potential in the opposite direction, indication means, and means controlled by the electric potential generated by any one of said thermo-electric devices in said control circuit arrangement for operating said indication means.

5. Heat indication apparatus for a plurality of elements comprising, in combination, a plurality of thermo-electric devices one for each of said elements, each of said thermo-electric devices placed to be controlled to generate an elec tric potential in response to abnormal heating of the corresponding one of said elements, a Wheatstone bridge circuit arrangement in which each of the four arms includes one of said thermoelectric devices connected to supply an electric potential in a given direction and also includes another of said thermo-electric devices connected to supply an electric potential in the opposite direction, indication means, and means controlled by the potential drop across opposite points of said bridge produced by electric potential generated by any one of said thermo-electrlc devices for operating said indication means in response to abnormal heating of the corresponding one .of said elements.

fi neat indication a paratus tor -a plurality of elements comprising, in combination, aplurality of therm'o-electricdevicesone for each of said elements, each of said thermo-electric devices placed to be controlled to generate an electric potential in response to abnormal heating of the corresponding one of said elements, a Wheatstone bridge circuit arrangement in which each of the four arms includes one .of said thermo-electric devices connected to supply an electric potentialin a given direction and also includes another of said thermo-electric devices connected'to'supply an electric potential in the opposite direction, means for periodically inserting an auxiliary electric potential in one of said arms of said bridge, code following means, means controlled by the voltage drop produced periodically across opposite points of said bridge by said auxiliary electric potential for periodically operating said code following means, means controlled by voltage drop produced across opposite points of said bridge by any one of said thermo electric devices in response to'abnormal heating of the corresponding one of said elements for constantly operating said code following means during the off periods of said auxiliary electric potential, and indication means controlled by said code following means.

'7. Heat indication apparatus for a plurality oi. elements comprising, in combination, a plurality of thernio-electric devices one for each of said elements, each of said thermo-electric devices placed to be controlled to generate an electric potential in response to abnormal heating of the corresponding one of said elements, a control circuit arrangement in which a given number of said thermo-electric devices are connected in series to supply an electric potential in a given direction and an equal number of said thermo-electric devices are connected in series with each other and with said given number of said thermo-electric devices to supply an electric potential in the opposite direction, first amplifying means for said electric potential in said given direction, second amplifying means for said electric potential in said opposite direction, indication means, means controlled by said first amplifying means for operating said indication means in response to electric potential generated by any one of said given number of electro-responsive devices, and means controlled by said second amplifying means for operating said indication means in response to electric potential generated by any one of said equal number of thermo-electric devices.

8. Heat indication apparatus for a plurality of elements comprising, in combination, a plurality of thermo-electric devices one for each of said elements, each of said thermo-electric devices placed to b controlled to generate an electric potential in response to abnormal heating of the corresponding one of said elements, a control circuit arrangement in which a given number of said thermo-electric devices are connected in series to supply an electric potential in a given direction and an equal number of said thermo-electric devices are connected in series with each other and with said given number of said thermo-electrio devices to supply an electric potential in the opposite direction, a first gas tube, a second gas tube, means for normally supplying a negative bias voltage to the grid of each of said gas tubes, means controlled by electric potential generated by any one of said given number of thermo-electric devices for making the grid of said first gas tube less negative, means controlled by electric REFERENCES CITED Potential generated by any we Said equal The following references are of record in the number of thermo-electric devices for making the file of this patent: grid of said second gas tube less negative, and indication means operated by means controlled 5 UNITED STATES PATENTS by said first and second gas tubes in response to Number Name Date electric potential generated by any one of said 2,126,115 Jordi Aug. 9, 1938 given number of thermo-electric devices or by 2,473,940 Clark V June 21, 1949 any one of said equal number of theme-electric 2,478,000 Miller Aug. 2, 1949 deViceS leSpectively.

L s JOHNSOLL Number Country Date LES'I'ER E. SPRAY. 01, 7 Germany Sept. 8, 1924 

